1. Field of the Invention
The present invention relates to the identification of a source of a signal such as, for example, one of a plurality of detectors for neutron and gamma emissions. The invention also relates to a method and system for monitoring neutron and gamma emissions from sources such as, for example, spent nuclear fuel.
2. Background Information
Many nuclear applications require the use of xe2x80x9cradiation hardxe2x80x9d signal cable. Unfortunately, this type of cable tends to be bulky and expensive. Many of these nuclear applications also require the measurement of a xe2x80x9cprofilexe2x80x9d of the radiation field. However, the drawbacks of radiation hard cable could limit some systems to use fewer sensors than desired to achieve these profiles. In some applications, this could necessitate the movement of large bulky detector systems, introducing undue hazard in the measurement process.
Measuring the gamma and neutron fields coming from a reactor core or from spent nuclear fuel assemblies (e.g., close packed, square arrays of some 200 or more evenly spaced fuel rods, typically twelve feet in height) are just two examples where space and access are at a premium. Furthermore, in each of these applications, there are compelling technical reasons for requiring a spatial profile of the fieldxe2x80x94along the height of the reactor core or along the height of the spent fuel assembly.
Application Ser. No. 08/851,237 discloses the use of miniature, temperature-resistant and radiation-resistant semiconductor detectors which permit simultaneous monitoring of the gamma and neutron emission rates from spent nuclear fuel. Arrays of semiconductor detectors may be used to obtain information from key axial locations to define the axial burnup profile for spent nuclear fuel assemblies. Use of the improved spent fuel monitoring apparatus results in significant reductions in cost and time for the measurements, as well as improved accuracy, safety and reduced radiation doses to personnel involved in spent nuclear fuel measurements. Nuclear detectors based on SiC semiconductors are capable of measuring gamma rays and neutrons simultaneously in a single, energy-resolved spectrum. Arrays of semiconductor detectors simultaneously measure neutron emission rates at key axial locations in order to define the shape of the fuel burnup profile. A string of miniature semiconductor neutron detectors simultaneously records data on a plurality of corresponding cables. The signals from those cables are multiplexed to provide independent data for each axial location, and may provide information on the entire axial burnup profile. The semiconductor detector arrays perform measurements within channels or on opposite flats of spent fuel assemblies.
Applications where neutron and/or gamma profile mapping are needed require an array of radiation sensors. In those situations, a count must be acquired from each detector location. Special radiation hard signal cables are often required, because of the high temperature and radiation environments which are present in those applications. These cables are quite costly. Hence, running a cable from each detector location becomes economically unattractive when more than a few locations are to be monitored. Furthermore, the resulting system is bulky and difficult to maneuver. The use of conventional multiplexing electronics is also impractical, since components made from silicon, like transistors, cannot withstand the environment.
Accordingly, there is room for improvement.
The present invention has been developed in view of the foregoing and other deficiencies of the prior art. This invention identifies the source of a signal from multiple detector sources. The method and system employ the time differential of two arriving signals to distinguish them from signals from other detectors, also connected to the same communication channel or cable. This reduces the number of cables required and is particularly important in applications where expensive, environmentally rugged cabling is required (e.g., spent fuel monitoring). This method permits the use of multiple detectors with a single cable, improves the quality of the data, significantly reduces the risk associated with certain measurements, and greatly reduces cost.
As one aspect of the invention, a method of determining which of a plurality of detectors transmitted a signal comprises connecting each of the detectors to a communication channel to transmit signals from each of the detectors over the communication channel; connecting the communication channel to a first receiver and a second receiver; receiving a first signal from the communication channel with the first receiver; receiving a second signal from the communication channel with the second receiver; introducing a unique delay between receipt of the first signal from the communication channel and receipt of the second signal from the communication channel for each of the detectors; measuring a delay between the first and second signals; and determining which of the detectors transmitted by associating measured delays with the unique delay.
Preferably, a cable having a first end and a second end is employed as the communication channel. The first signal is received from the first end, and the second signal is received from the second end of the cable. A plurality of first lengths are provided between the first end and the detectors, and a plurality of second different lengths are provided between the second end and the detectors, in order to provide a unique predetermined difference in length between the first and second lengths for each of the detectors.
As another aspect of the invention, a system for identifying a source of a signal comprises a communication channel; a plurality of detector means, each of which source a signal to the communication channel; means for receiving a first signal and a second signal from the communication channel, which includes means for introducing a unique delay between receipt of a first signal from the communication channel and receipt of a second signal from the communication channel for each of the detectors; means for measuring a delay between the first and second signals received from the communication channel; and means for determining from the measured delay which of the detector means sourced the signal.
As a further aspect of the invention, a system for monitoring a source of neutron or gamma emissions comprises a communication channel; a plurality of detector means for the neutron or gamma emissions, with each of the detector means for sourcing a signal related to the emissions to the communication channel; means for receiving a first signal and a second signal from the communication channel, which includes means for introducing a unique delay between receipt of a first signal from the communication channel and receipt of a second signal from the communication channel for each of the detectors; means for measuring a delay between the first and second signals received from the communication channel; and means for determining from the measured delay which of the detector means sourced the signal, in order to count the neutron or gamma emissions therefor.